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I seem to have run across a dispute about whether or not the various pulleys involved with a timing belt should spin freely or not.

For example, in this video the anonymous Internet expert says that a good t-belt pulley spins freely. Also, @Ben from this site says the same.

However, I ran across other opinions stating the exact opposite:

pulleys in good condition will stop very shortly after you spin them by hand. New pulleys will stop immediately. Natural friction of the grease inside the bearing caps are what slows down rotation.

What I've found the most convincing so far is this video in which a guy presses brand new bearings into his t-belt idler pulley and gives it a little spin and it stops very quickly.

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I think both are stating the same thing, but telling it differently. Basically what I mean by this is, spinning freely does not need to mean it will continue to spin without stopping, but rather spins without binding. The main thing to look for in these pulleys is if, when turned, they are completely smooth to the touch and turn without much resistance, they are probably in good shape. The other thing to check for is to see if there is any movement in the bearings from side to side or have any play in it. The bearing should be fairly solid without any type of deflection. The idea that grease will slow up the bearing rotation is completely understandable and makes solid sense. I really just think the difference here is a matter of semantics.

EDIT: One thing I neglected to mention is changing out pulleys during normal t-belt replacement is a good thing. Most t-belt kits come with pulleys. Just like a water pump, I consider changing out the pulleys to be routine maintenance during a t-belt replacement. Just like with the water pump, it only makes good sense to replace them while you're in there changing out the belt. They may last you another 60-100k miles, but why chance it. The cost is by far cheaper than the alternative of a completely destroyed engine.

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  • What the guy in the first video shows is a pulley that he spins and it keeps spinning maybe twenty times before it stops, and that seems to be what some people are intending, although what you are saying makes good sense.
    – Robert S. Barnes
    Nov 13, 2016 at 18:18
  • @RobertS.Barnes new pulleys sometimes come with a grease in them that "melts" as the pulley spins. You can replace pulleys as a precaution or to save time and having to repull covers in the future. but if the pulley isn't making noise and spins smoothly by hand there isn't a real reason to replace it.
    – Ben
    Nov 13, 2016 at 21:46
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    @Ben At the moment I think the tensioner, spring and idler are probably fine, and once I start my process of elimination I'll stumble on something really minor and stupid that I did wrong which will make me go duh! Like maybe I overtightened the PS / AC belt or didn't evenly tighten down the WP pulley bolts evenly or some other silly novice mistake.
    – Robert S. Barnes
    Nov 13, 2016 at 22:01

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